Cooking devices are being equipped to an increasing extent with a steam generating system for improving the results of the cooking process with the help of the damp air which then ensues in the cooking area. Such cooking devices are, for example, combination steamers, baking-ovens or hot-air ovens. They serve, in particular, for the purposes of preparing food for consumption. On the one hand hereby, it is possible to produce steam by means of a steam generator located externally of the cooking area and then feed this steam into the cooking area through a connecting member.
However, in another concept of increasing interest, the steam is not fed into the cooking area from an external source but is produced directly in the cooking area. To this end, water is supplied to the cooking area and distributed therein in different forms and is thus evaporated by the hot environment.
For this purpose, water supply pipes are employed in accordance with the concepts known from EP 0 233 535 B1, EP 0 383 366 B1 or EP 0 640 310 B1 for example, said pipes supplying the water to the hub of the fan in a centrifugal fan. Due to the fact that the hub is rotating, the water is fed from the hub to the impeller blades of the fan by centrifugal force and there, the water is decomposed insofar as possible into drops which should then evaporate in the hot atmosphere of the cooking area. Hereby, the hub is approximately cylindrical in the case of EP 0 233 535 B1 and EP 0 383 366 B1, whilst EP 0 640 310 B1 proposes a pre-atomising member which is approximately spherical in shape and thus possesses a convex surface and hence is better at distributing the droplets.
In each of the respective proposals in accordance with DE 197 31 544 A1 and DE 41 31 748 C2, there are provided pre-atomising members in the form of disks which are located within the radial flow impeller and rotate with the hub. The disks are axially symmetrical. The water is delivered externally to the outer periphery of the disk in a radial direction in the case of DE 197 31 544 A1, whereas it impinges a very small part of the disk at an angle in DE 41 31 748 C2.
Herein, the heating of the atmosphere in the cooking area is effected by electrical heating elements or else by means of heat exchanger pipes through which there flows a hot medium so that they too function as a heating element. These heating elements are usually disposed directly in the flow path of the impeller in order to distribute the ensuing heat in a uniform manner.
Similar concepts are proposed in both EP 0 244 538 B1 and EP 0 523 489 B1, whereby here, the water is supplied internally in axially parallel manner to the interior of the hub from outside the cooking area through central passages in the hub, from where it is likewise distributed outwardly onto the fan blades. So as to make this possible, complicated seals and co-rotating clamping devices must be provided in order to maintain the stability of the cup-like hub (EP 0 244 538 81) or the cone-like extended hub (EP 0 523 489 B1), to prevent water seepage at unintentional places and in order to ensure proper functioning.
The disadvantage with all of the aforementioned concepts is that the peripheral speed of the described hub components is naturally relatively very low due to the proportionately small diameter of the hub. This relatively low peripheral speed leads to a relatively small centrifugal force and thus to a non optimal distribution of the water droplets which remain relatively large. If one were to increase the rotational speed of the fan i.e. the rotational speed of the fan motor in the fan in order to improve the effectiveness of the arrangement, then this would lead to the need for higher powered motors thereby increasing the costs both for the cooking device and for the operation thereof, this being something that is not desired. In addition, the higher air speeds then ensuing in the cooking area are neither necessary nor desirable.
Constructions have therefore been proposed in EP 0 457 971 B1, DE 40 13 596 C2 and DE 41 25 696 C1 wherein the water is not conveyed to the hub, but rather, is introduced into the air inlet region of the fan and distributed from there. Thereby, the water runs over a complicated cascaded distribution structure in EP 0 457 971 B1, it impinges directly on the blades in DE 40 13 596 C2, and, in DE 41 25 696 C1, it is proposed that the water be distributed individually via a plurality of water supply devices and delivered in front of the respective heating elements. The disadvantage of these constructions is the relatively high expenditure and the complexity of the final installation. This leads to high costs and, in particular, makes cleaning of the corresponding cooking devices substantially more difficult. In addition, the uniformity of the distribution process and thus the efficiency of the arrangements are unsatisfactory.